The invention relates to a tape recorder having a group of write heads, which are arranged like a matrix in rows and columns. The invention is based on a tape recorder according to the precharacterizing clause of Claim 1.
In the following text, the term tape recorder means any apparatus in which signals, data or information are recorded in digital form on a magnetic tape, and/or are read from this magnetic tape. Independently of this, these apparatuses may also have other functions, for example they may be combined with an electronic camera or with a computer. In the latter case, such apparatuses are also called xe2x80x9cdata streamersxe2x80x9d.
The publication xe2x80x9cTowards the Multitrack Digital Video Tape Recorderxe2x80x9d by Francois Maurice in xe2x80x9cThe Magnetic Society of Japanxe2x80x9d 1991, Volume 15, pages 389 to 394, discloses a tape recorder in which a large number of data and/or signal tracks are recorded on a magnetic tape using the longitudinal track recording method. In the apparatus disclosed in this document, the data tracks are written simultaneously by means of a matrix head. In an exemplary embodiment of this apparatus, up to 80 parallel tracks are written with a width of 7 xcexcm without any guard tracks, that is to say without any intermediate space between the individual tracks.
EP 0 764 943 discloses a tape recorder having a matrix head. The matrix head comprises a ferrite block which has grooves in the longitudinal and transverse directions and to which a thin-film structure is applied, which has a column at the intersections of the grooves. Insulating, electrical conductors are located in the grooves in the ferrite block. When a current flows through the conductors, then a magnetic field occurs in the external area in the region of the columns. The ferrite block thus combines a large number of write heads, which are produced jointly in a single process.
A magnetic field can be produced in any individual column by current switching and correct timing of the association of currents in the row and column directions. To this end, a signal which is applied to the data channels and which initiates currents in the row lines is correlated in time with a rapidly switched selection current in the column lines. In the situation where the resultant magnetic fields which are caused by the currents in the row and column lines reinforce one another in the external area of a column, a magnetic tape which is present at the relevant column is remanently magnetized. In the converse case, where the said magnetic fields cancel one another out in the external area, a magnetic tape which is present at the relevant column is not remanently magnetized.
On the one hand, such a system allows a high data rate to be recorded at a high storage density on a magnetic tape. On the other hand, this system places very stringent requirements on the driver circuit for the matrix head, as is made clear in the analyses below.
In the case of a matrix head having eight data lines which define the rows of the matrix head, and having ten selection lines which define the columns of the matrix head, and at a data rate of 125 kbps per track, a complete sequence of the selection lines is completed after 4 xcexcs. This means that only 400 ns are available for writing for each column in the matrix head. In this case, it must also be remembered that the current flowing in the selection line has to reach its maximum value in both one direction and in the other direction during this time interval, as will be explained in more detail further below. The currents in the data lines are xc2x1100 mA and those in the selection lines are xc2x1200 mA. In order to ensure that the magnetic tape is always magnetized reliably and uniformly, the values of the currents must be maintained accurately, and they must be switched quickly and at exact times, matched to one another. In practice, it has been found to be expedient for the currents to rise to the their respective maximum values, and to fall from the respective maximum values to zero, within 20 ns.
Based on this, one object of the invention is to provide a tape recorder which satisfies all these requirements and, furthermore, whose circuitry is less complex than the known solutions.
This object is achieved by a tape recorder according to Claim 1. The solution according to the invention is characterized in that a common row return line is provided to which all the data lines are connected, and in that a common column return line is provided to which all the selection lines are connected.
The column return lines have the advantage that this reduces the circuit complexity for a driver circuit.
Means may expediently be provided in order to switch column lines through which current is not being passed to a high impedance. This advantageously ensures that a current is only ever flowing in a single column of the matrix head. This has the advantage that it is impossible for any uncontrolled magnetic fields to occur at the individual write heads in the matrix head, so that the conditions for magnetization of the magnetic tape are always defined.
In order that the current can flow in both directions in the associated column lines, it can be expedient to provide for the capability to connect the column return line selectively to earth or to an operating voltage.
It is particularly advantageous if the common row return line is clamped to a voltage whose magnitude corresponds to approximately half the maximum magnitude of the voltage which is applied to the column return line. This results, in a particularly simple manner, in the currents in the column lines being twice as great as those in the data lines.
In one exemplary embodiment of the invention, in which the data in the data lines are coded without any direct current, it is advantageous if the common row return line is connected to a capacitor. It is particularly advantageous if the capacitor is connected, with low impedance, by means of a suitable network to a predetermined operating voltage.
Finally, a voltage supply can also be provided which regulates the supply voltage of the driver circuit in such a way that the magnetic fields produced by the matrix head are matched to different tape materials. Different characteristics of different matrix heads can also be compensated for in the same way, and power losses in the driver circuit can be minimized. In this context, it should be noted that, owing to the special manufacturing process, it is virtually impossible to distinguish between the characteristics of individual write heads which are part of a single matrix head. On the other hand, significant differences may occur between different matrix heads.
One particular advantage of the tape recorder according to the invention is that further matrix heads can be connected to the driver circuit without significant additional complexity. Further advantages of the invention are the subject matter of dependent claims.